1. Field of the Invention
The present invention relates to a method by which a multi mode mobile terminal (hereinafter referred to as a “wireless terminal”) that can access at least one or more of heterogeneous mobile communication systems detects a candidate system that can be accessed from a current location and performs handover, and a location service server (LCS) therefor. More specifically, the present invention relates to a method of providing and obtaining information by a multi mode terminal, an operation method of a location service server, and an apparatus therefor, by which battery consumption, which occurs when a wireless terminal that can access a plurality of mobile communication systems activates multi-standard modems in the wireless terminal in order to detect candidate systems when performing handover between heterogeneous networks, can be prevented, and a time taken for detecting candidate systems can be reduced.
2. Description of the Related Art
In beyond 3rd generation (B3G) and 4th generation (4G) mobile communication structures, one of the most important research topics is to implement seamless connection in an optimum system with respect to the current environment of a service subscriber through interoperation when services areas of mobile communication systems having different characteristics are overlapping each other.
For this handover between heterogeneous networks, a wireless terminal needs to detect a candidate system in addition to a system to which the wireless terminal is currently connected.
The methods of detecting candidate systems by a wireless terminal can be divided roughly into two methods. The first method detects a candidate system by activating all modems in the wireless terminal or activating the modems periodically. The second method detects a candidate system with respect to the location of a wireless terminal or a wireless access base station.
In the first method, candidate systems are detected continuously by activating continuously all multi-standard modems in a wireless terminal. However, in this case, the battery consumption of the wireless terminal increases because all modems are activated.
In another case of the first method, candidate systems are detected by activating and inactivating multi-standard modems in the wireless terminal periodically. In this case, the battery consumption can be reduced (though the battery consumption problem still exists), but there still is a problem in that the time taken for detecting candidate systems increases because modems are periodically activated and/or inactivated.
In particular, if the wireless terminal is a software defined radio (SDR)-based terminal, instead of using the multi-standard modems, one modem is reconfigured by software to perform mode conversion and any conventional technologies falling within the first method cannot be used basically. Accordingly, a method by which an SDR terminal can detect a candidate system is needed.
In the second method of detecting a candidate system, the location of a wireless terminal has to be estimated. This can be done by Cell-ID, enhanced observed time difference (E-OTD), observed timed difference of arrival (OTDOA), and assisted global positioning system (A-GPS, hereinafter referred to as “GPS”).
Generally the distance between a wireless terminal and a wireless access base station is estimated by using a location tracking technology, and a candidate system is selected based on the distance. More specifically, if a wireless terminal is located within a theoretical service area of a predetermined wireless access base station, that is, if the distance between the wireless terminal and the wireless access base station is small, the wireless terminal selects the corresponding system as a candidate system.
Theoretically, assuming that there are no obstacles in a propagation environment, a higher signal intensity can be obtained by decreasing the distance between a terminal among a plurality of mobile communication terminals and the wireless access base station. However, in an area having many elements in the propagation environment, such as a city center, the accuracy of estimating a signal intensity with respect to the distance between the terminal and the wireless access base station is not guaranteed. Accordingly, in the city central area where service areas of mobile communication systems having different characteristics are overlapping each other, there is a problem in that selection of a candidate system with respect to the distance between a terminal and a wireless access base station may not be reliable.